1. Field of the Invention
The present invention relates to a heat-resistant structural body, a halogen-based corrosive gas-resistant material and a halogen-based corrosive gas-resistant structural body.
2. Description of the Related Art
As wirings in the semiconductors and liquid crystal panels become finer, fine workings with dry processings are progressing. With the demand for such fine workings, a halogen-based corrosive gas is used as a film-forming gas or an etching gas for the semiconductors and the like. It is known that aluminum nitride exhibits high corrosion resistance against such a halogen-based corrosion gas. Therefore, members having aluminum nitride on their surfaces have been used in semiconductor-producing apparatuses, liquid crystal panel-producing apparatuses and the like.
When aluminum contacts the air, its surface is oxidized to form a thin oxidized film. Since this oxidized film is an extremely stable passive phase, the surface of aluminum could not be nitrided by a simple nitriding method. Under the circumferences, the following methods have been developed to modify the surface of aluminum and form aluminum nitride thereon.
JP-A-60-211061 discloses a method in which after the inner pressure of the chamber is reduced to a given level, and hydrogen or the like is introduced thereinto, discharging is conducted to heat the surface of a member such as aluminum to a given temperature, further argon gas is introduced and discharging is conducted to activate the surface of the member, and the surface of the aluminum member is ionically nitrided through introducing nitrogen gas. In addition, JP-A-7-166321 discloses a method in which a nitriding aid made of aluminum powder is contacted with the surface of the aluminum, and aluminum nitride is formed on the surface of aluminum through heating in a nitrogen atmosphere.
An aluminum nitride film itself has high heat resistance, high heat-cycling durability and high Vickers hardness. However, in such a technique that forms an aluminum nitride film on an aluminum substrate, the aluminum nitride film tends to peel off from the substrate when heat-cyclings are applied, depending on a difference in thermal expansions between the obtained aluminum nitride film and metallic aluminum or a state of an interface between the substrate and the aluminum nitride film.
It is an object of the present invention to improve heat-cycling durability of a structural body in which a nitrided material is provided on a substrate containing at least metallic aluminum.
It is another object of the present invention to further improve halogen-based corrosive gas-resistance of a structural body comprising a substrate containing at least metallic aluminum and a nitrided material formed on the substrate.
It is yet another object of the present invention to provide a nitrided material having high resistance against hydrofluoric acid and a halogen-based corrosive gas and high heat-resistance.
The present invention relates to a heat-resistant structural body comprising a substrate containing at least metallic aluminum and a nitrided material formed on the substrate, wherein the nitrided material is composed mainly of an aluminum nitride phase and a metallic aluminum phase.
The present inventors found that such a lamination structural body had higher heat resistance, especially heat-cycling durability than a structural body where an aluminum nitride film was formed on metallic aluminum. The reason of this is not clear, but it is considered that since the film is the mixed phase of aluminum nitride phase and the metallic aluminum phase, the film has a closer expansion coefficient to aluminum of the substrate than the aluminum nitride film does, so that stress on the interface between the substrate and the nitrided material is relaxed.
In the present invention, the nitrided material may be composed mainly of the aluminum nitride phase and the metallic aluminum phase, and other crystal phase or amorphous phase may exist. However, the total amount of the aluminum nitride phase and the metallic aluminum phase is preferably not less than 80 mol %, and more preferably not less than 90 mol %.
In a preferred embodiment, the nitrided material contains at least one metallic element selected form Group 2A, Group 3A, Group 4A and Group 4B in Periodic Table.
In a particularly preferred embodiment, the nitrided material contains at least one metallic element selected from Group 2A, Group 3A and Group 4A in Periodic Table. By incorporating such a metallic element, resistances of this structural body against the halogen-based corrosion gas, especially fluorine-based corrosive gas was found to be significantly improved.
That is, it is known that the halogen-based corrosive gas and its plasma used in semiconductor producing processes etc. exhibit strong chemical and physical interactions with the substrate to be treated. Silicon, silicon oxide and the like are etched by using these interactions. The present inventors exposed a various kind of the structural bodies to the halogen-based corrosive gas, and, as a result, found that the durability of the structural body against chemical corrosion of the plasma of the halogen-based corrosive gas was improved by incorporating at least one metallic element selected from Group 2A, Group 3A, Group 4A and Group 4B in Periodic Table into the nitrided material. That is, the present inventors found that the above-mentioned metallic element contained in the nitrided material reacts with the halogen gas and its plasma to accelerate a formation of a passive film on the surface of the nitrided material. The corrosion was inhibited from extending into the nitrided material by the passive film.
The passive film itself is physically etched in the plasma of the halogen-based corrosive gas by receiving a bombardment of the high-energy gas. However, at least one metallic element selected from Group 2A, Group 3A and Group 4A in Periodic Table existing in the nitrided material and the underlying substrate reproduce the passive film by diffusing toward the surface of the nitrided material. Therefore, the number of reproducing the passive film, or the resistivity was found to depend on the concentrate of the above-mentioned metallic element(s) in the film and the substrate.
Summarizing the findings in the above, the structural body of the present invention has two features:
(1) the nitrided material on the surface absorbs a difference between the substrate in the thermal expansions as the mixed film of the aluminum nitride phase and the metallic aluminum phase; and
(2) by incorporating at least one metallic element selected from Group 2A, Group 3A and Group 4A into Periodic Table at least in the nitrided material, when the structural body is exposed to the halogen-based corrosive gas and its plasma, especially to the fluorine-based gas and its plasma, the chemical corrosion resistance against these gases and plasmas is improved by the passive film formed on the surface by halide, which is formed with the metallic element.
By combining these features, the structural body of the present invention is extremely stable even under such a circumstance that exposes the structural body to the halogen-based corrosive gas and its plasma, especially under a circumstance that causes such exposure of the structural body at a high temperature of not less than 200xc2x0 C.
Among the metallic element selected from Group 2A, Group3A and Group 4A in Periodic Table, the nitrided material preferably contains magnesium, since magnesium acts effectively in the process of forming the nitride film as well as it is one of metal elements having an especially low vapor pressure of a fluoride formed upon exposing to the fluorine-based gas.
In a preferred embodiment, the nitrided material contains 1-10 atm % of at least one metallic element selected from Group 2A, Group 3A and Group 4A in Periodic Table. More preferably, the nitrided material contains not less than 3 atm % of the metallic element(s).
Moreover, in a preferred embodiment, the substrate contains 1-10 atm % of at least one metal selected from Group 2A, Group 3A and Group 4A in Periodic Table. When the passive film formed on the nitrided material is gradually derogated by a physical corrosion, the metallic element gradually moves from the substrate to the nitrided material, and further to the passive film to regenerate the passive film. From this viewpoint, the substrate containing not less than 3 atm % of the metallic element is more preferable.
The present inventors also found that if the nitrided material contained a metallic element selected from Group 4B in Periodic Table, the metallic element tended to evaporate upon being exposed to the halogen-based corrosive gas and its plasma to readily cause the chemical corrosion.
Accordingly, from this viewpoint, the amount of the metallic element selected from Group 4B in Periodic Table is preferably not more than 0.5 atm %, and the amount of silicon atoms is substantially not more than 0.5 atm % in the nitrided material. More preferably, substantially no silicon atoms is contained in the nitrided material.
The terms xe2x80x9cnitrided materialxe2x80x9d of the present invention refers to a material obtained from a nitriding process of metallic aluminum, and more particularly, a material obtained by partially nitriding metallic aluminum. Therefore, a part of the metallic aluminum is not nitrided to remain in the nitrided material.
The proportion of the aluminum nitride phase in the nitrided material is preferably 10-90 mol %, when the sum of the aluminum nitride phase and the metallic aluminum phase is set to 100 mol %.
If the proportion of the aluminum nitride phase is not more than 10 mol %, the nitriding may be performed insufficiently to cause low hardness of the nitrided material and low resistivity against the physical corrosion. From this viewpoint, the proportion of the aluminum nitride phase is further preferably not less than 20 mol %.
If the proportion of the aluminum nitride phase excess 90 mol %, the durability of the structural body against heat cycling is degraded and the nitrided material tends to peel off. From this viewpoint, the proportion of the aluminum nitride phase is further preferably not more than 80 mol %.
In order to exert the physical and chemical resistivity of the nitrided material, the thickness of the nitrided material is preferably not less than 3 xcexcm. The thickness is more preferably not less than 10 xcexcm. The thickness of the nitrided material has no particular upper limit.
Other metallic element, for example, the above-mentioned metallic element(s) selected from Group 2A, Group 3A, Group 4A and Group 4B in Periodic Table may be contained in the nitrided material. Such metallic element(s) other than aluminum may be contained in the form of metal nitride(s), but it is particularly preferable that it is (they are) dissolved as an alloy in aluminum.
A type of substrate is not limited, but a metallic aluminum-containing metal is preferred. Pure metallic aluminum and an alloy of metallic aluminum and other metal(s) can be recited by way of example of such a metal. The other metal is not restricted, but includes the above-mentioned metallic element(s).
In order to achieve higher heat resistance, the substrate may also be an intermetallic compound containing aluminum atoms, and a composite material of a metallic aluminum-containing metal and a metallic aluminum-containing intermetallic compound. Al3Ni, Al3Ni2, AlNi, AlNi3, AlTi3, AlTi, Al3Ti may be recited by way of example of the intermetallic compound containing aluminum atoms. Pure metallic aluminum and the alloy of metallic aluminum and other metal(s) may be recited by way of example of the metallic aluminum-containing metal.
Furthermore, the substrate is preferably a composite material of the metallic aluminum-containing metal and a low thermal expansion material, and is preferably a composite material of the above-mentioned intermetallic compound and the low thermal expansion material. In this case, the low thermal expansion material is preferably at least one low thermal expansion material selected from AlN, SiC, Si3N4, BeO, Al2O3, BN, Mo, W and carbon. The content of the low thermal expansion material is preferably 10-90 vol %.
A member comprising a metal, a ceramic material, an intermetallic compound, a composite material or the like having its surface coated with aluminum or an aluminum alloy may be used as a substrate.
The present invention relates to a halogen-based corrosive gas-resistant structural body comprising a substrate containing at least metallic aluminum and a nitrided material formed thereon, wherein the nitrided material is composed mainly of aluminum nitride phase and a metallic aluminum phase, and the nitrided material contains 1-10 atm % of at least one metallic element selected from Group 2A, Group3A and Group 4A in Periodic Table.
The present invention also relates to a halogen-based corrosive gas-resistant material, which is composed mainly of an aluminum nitride phase and a metallic aluminum phase and contains 1-10 atm % of at least one metallic element selected from Group 2A, Group 3A and Group 4A in Periodic Table. Unlike the above-mentioned structural body, this material may not necessarily be in a film form. It may take one of various kinds of forms such as a plate, a film or a sheet separated from the substrate.
The present invention further relates to a halogen-based corrosive gas-resistant structural body comprising a substrate containing at least metallic aluminum, a nitrided material formed on the substrate and a passive film formed thereon, wherein the nitrided material is composed mainly of an aluminum nitride phase and a metallic aluminum phase and contains 1-10 atm % of at least one metallic element selected from Group 2A, Group 3A and Group 4A in Periodic Table, and the passive film contains mainly an aluminum nitride phase, a metallic aluminum phase and a fluoride phase of the above-mentioned metallic element.
The present invention still further relates to a halogen-based corrosive gas-resistant structural body, which comprises a halogen-based corrosive gas-resistant material and a passive film formed thereon, the material being composed mainly of an aluminum nitride phase and a metallic aluminum phase and containing 1-10 atm % of at least one metallic element selected from Group 2A, Group 3A and Group 4A in Periodic Table, and the passive film containing mainly an aluminum nitride phase, a metallic aluminum phase and a fluoride phase of the above-mentioned metallic element.
Since the above-mentioned metallic element has a lower vapor pressure than that of metallic aluminum in a fluorinating process, a passive film of the obtained fluoride has high stability.
For the above-mentioned reason, the compositional proportion of the aluminum nitride phase is preferably 30-80 mol %, when the sum of the aluminum nitride phase and the metallic aluminum phase in the passive film is taken as 100 mol %.
The compositional proportion of the at least one metallic element selected from Group 2A, Group3A and Group 4A in Periodic Table is preferably 1-10 mol %.
Next, a method of producing the heat-resistant structural body and the halogen-based corrosive gas-resistant structural body according to the present invention will be described.
In order to produce these structural bodies, a substrate containing metallic aluminum is heated under high vacuum degree, more preferably under the presence of a material which contains at least one metal selected from Group 2A, Group 3A and Group 4A in Periodic Table or a vapor thereof, followed by heating in nitrogen atmosphere without any other treatment. It is considered that an alumina passive film on the surface of the aluminum substrate is removed by the heat treatment under high vacuum degree, and thus the surface is readily nitrided. Such a process itself is also described in Japanese Patent Application No. 11-059011 (Priority Date Feb. 4, 1999: JP-A-2000-290767).
In order to produce the heat-resistant structural body and the halogen-based corrosive gas-resistant structural body of the present invention, the substrate is necessary to have the heat treatment under vacuum of not more than 10xe2x88x923 torrs, and preferably not more than 5xc3x9710xe2x88x924 torrs.
The lower limit of the pressure in vacuum is not particularly limited, but it is preferably 10xe2x88x926 torrs, and more preferably 10xe2x88x925 torrs. A larger pump and a higher-vacuum tolerant chamber are necessary to achieve a higher vacuum degree, thereby raising the cost. However, even when the vacuum degree is less than 10xe2x88x926 torrs, the nitride-forming rate is not particularly enhanced as compared to that of 10xe2x88x925 or 10xe2x88x926 torrs and so it is not practically useful to reduce the vacuum degree below 10xe2x88x926 torrs.
The lower limit of the temperature of the heat treatment is not particularly limited as far as the nitrided material can be formed on the surface of the substrate. However, to form the nitrided material easily and shortly, the lower temperature limit is preferably 450xc2x0 C., and more preferably 500xc2x0 C.
The upper limit of the temperature of the heat treatment is not also particularly limited, either, but it is preferably 650xc2x0 C., and more preferably 600xc2x0 C. By so setting, a thermal deformation of the substrate containing aluminum can be prevented.
A nitrogen-containing gas, such as N2 gas, NH3 gas and mixed gas such as N2/NH3 gas may be used as the nitrogen atmosphere in the heating/nitriding treatment. In order to form a thick nitrided material on the heat-treated substrate in a relatively short time, the gas pressure of the nitrogen atmosphere is preferably set at not less than 1 kg/cm2, more preferably in a range from 1 to 2000 kg/cm2, and particularly preferably in a range from 1.5 to 9.5 kg/cm2.
The heating temperature in the heating/nitriding treatment is not particularly limited as far as the nitrided material can be formed on the surface of the substrate. However, to form a relatively thick nitrided material in a relatively short time, the lower limit of the heating temperature is preferably 450xc2x0 C. as mentioned above, and more preferably 500xc2x0 C.
Further, the upper limit of the heating temperature in the heating/nitriding treatment is preferably 650xc2x0 C., and more preferably 600xc2x0 C. By so setting, a thermal deformation of the substrate can be effectively prevented.
The nitrided material thus formed on the surface of the substrate is not necessarily in the form of a layer or a film. That is, the form of the nitrided material is not limited as far as it is formed in such a state that it can afford corrosion resistance on the substrate itself. Therefore, the form includes such a state that fine particles of the nitrided material are densely dispersed or the composition of the nitrided material inclines toward the substrate with an interface between the nitrided material and the substrate being unclear. In fact, it is most preferable that the nitrided material is continued in the form of a layer or a film.
The concentration of oxygen in the nitrided material is preferably not more than two third of that in the substrate.
When the structural body of the present invention is to be manufactured, a substrate is placed on a sample table inside a chamber equipped with a vacuum device. Next, this chamber is evacuated with the vacuum pump until a given vacuum degree is achieved. Then, the substrate is heated with a heater, such as a resistant heating element placed in the chamber, until a given temperature is achieved. The substrate is held at this temperature for 1 to 10 hours.
After the heating treatment, the interior atmosphere of the chamber is replaced with a nitrogen gas by introducing the nitrogen gas or the like into the chamber. By adjusting the input power of the heater, the substrate is heated to a given temperature. Then, the substrate is held at this temperature for 1 to 30 hours.
After the given time has passed, the heating/nitriding treatment is terminated by stop heating and introducing the nitrogen gas. Then, the interior atmosphere of the chamber is cooled down, and the substrate is taken out from the chamber.
The structural body and the halogen-based corrosive gas-resistant material of the present invention can be used as a component in the semiconductor-producing apparatuses, the liquid crystal-producing apparatuses, the automobiles, etc. Further, the structural body of the present invention has excellent heat emission property. Therefore, the structural body can be favorably used in a heat emission component requiring the heat emitting property.
The halogen-based corrosive gas-resistant material and the halogen-based corrosive gas-resistant structural body according to the present invention have superior corrosion resistance against chlorine-based corrosive gases such as Cl2, BCl3, ClF3 and HCl, fluorine-based corrosive gases such as a ClF3 gas, a NF3 gas, a CF4 gas, WF6 and SF6, and plasmas thereof. In addition, the ambient temperature during the exposure to such a gas or plasma may be in a wide range from room temperature to 800xc2x0 C. Particularly, the structural body and the material of the present invention have superior corrosion resistance even in a high temperature region of 200-800xc2x0 C.